The invention concerns a method as well as a device for coating substrates.
Particular but not exclusive significance is attributed to the coating of arched surfaces of spectacle lenses or lenses having one or more layers, especially with scratch-proof coatings and uniform, glare-reducing multiple layers.
According to DE 39 31 713 C1, work pieces, in particular plastic lenses, are provided with an abrasion-resistant protective layer by placing them in the center region of a discharge space formed by two electrodes in free-floating fashion with regard for the electrical potential. Because, in the “plasma space”, the distribution of charge density is as independent of distance as possible, in contrast to the dark spaces directly next to the electrodes. The gas discharge is produced by applying a radio frequency field between the electrodes. This method has the disadvantage that the two sides of the substrate are coated differently, as one side always faces the grounded electrode and the plasma has other properties there than in the vicinity of the electrode launching the radio frequency.
Application WO 96/27690 describes a PECVD (“Plasma Enhanced Chemical Vapor Deposition”) method and a device for the two-sided coating of substrates, preferably spectacle lenses, by means of microwave excitation. A distinct plasma is used for each surface to be coated. In order to keep the heat load of the substrate low, the use of a pulsed discharge is recommended. No mention is made of which uniformities can be obtained in the coating and how they can be influenced.
Application WO 95/26427 A1 describes a PICVD method and a device for producing uniform coatings on lenses made of glass or plastic, in which the substrate surface to be coated is arranged opposite to the gas passage surface of a gas shower. In a preferred embodiment, the gas shower is developed as a zone shower by means of which locally different gas flows arise on the substrate. Individual microwave and gas flow parameters are used for each substrate form. Although uniformities that are adequate for anti-glare coatings as well are obtained, the determination of individual process parameters and their control is very costly.
A method and a device for the exterior coating of lamps is described in DE 196 52 454 A1. Damage caused by the microwaves to the lamp to be coated is prevented by selecting a microwave output launched into the microwave reactor that is greater than or equal to a threshold value at which a plasma having reduced permeability to microwave radiation arises. The microwaves are therefore shielded by the plasma. No statement is made about the layer uniformities that can be obtained.
A diamond coating method for the partial diamond coating of drills and sealing rings using UHF or microwaves is described in U.S. Pat. No. 5,645,645.
EP 0 326 998 B1 describes a method for the microwave-CVD coating of flat substrates.
In the devices according to U.S. Pat. No. 5,645,645 or EP 0 326 998 B1 there is an interplay of conventional tuning elements in the form of metallic slides and perforated metal plates. The conventional tuning elements serve to match impedance, which results in a higher microwave intensity. The structure of the microwave dispersion is not changed as a result, it is only shifted or intensified. In EP 0 326 998 B1, the perforated metal plate serves only to scatter the reaction flow. In the device according to U.S. Pat. No. 5,645,645, the perforated plate forms the launch site for the plasma and has an effect on the microwaves that is similar to a shield.